Equilibrium phase relationships in the system CaO-P2O5-H2O-CO2 at 2000 bars H2O pressure and up to 10 wt. % are under investigation using hydrothermal synthesis techniques. The stability of the mineral phases, the composition of the solution and mineral phase are being characterized by wet chemical gas chromatography, and x-ray diffraction techniques. Using previously determined phase relationships in the CaO- P2O5-H2O system mineral extracted from bones teeth and pathologically calcified tissues are being systematically examined.